1. Field of the Invention
The present invention relates to a technique for producing a highly convoluted surface on a prosthetic device.
Throughout the specification, the terms "aspherical" and "non-spherical" are used interchangeably and are intended to mean other than the spherical form.
2. Description of the Prior Art
There are a number of design criteria which have long been sought for the ideal segmental bone replacement implant. Three of these criteria are foremost: (1) the implant should last the lifetime of the patient without loss of function or initiating any adverse process response; (2) the implant should be designed to restore the normal function of the bone in which it is implanted; and (3) the implant must be producible on a commercial scale. To satisfy the foregoing criteria, it is necessary not only that the implant support the imposed load, often of a fluctuating nature, but also that the interface between the implant and the bone withstand the load requirement. This must be achieved on a regular and continuing basis.
A plastic cement such as polymethyl methacrylate is often used to affix the implant to the bone as well as to improve the fit between the implant and the bone. In another instance, prosthetic devices have been provided with porous coatings which fittingly mate with the bone and invite bone ingrowth such that, after a period of time, the prosthesis becomes integrated into the bone structure. Typical of such coatings are the disclosures in U.S. Pat., Nos. 3,855,638 and 4,206,516 to Pilliar, U.S. Pat. No. 4,156,943 to Collier, and U.S. Pat. No. 4,612,160 to Donlevy et al.
Ceramic coatings have also been used to good effect and are particularly desirable because of the affinity between the bone and ceramic materials such as alumina (A1.sub.2 O.sub.3). Typical of the prior art in this regard are U.S. Pat. No. 4,145,764 to Suzuki et al and U.S. Pat. No. 4,483,678 to Nishio et al which are particularly concerned with dental implants and 4,309,488 to Heide et al and 4,846,837 to Kurze et al which more broadly disclose implantable bone replacement material for use throughout the body as appropriate.
It was in light of the prior art as just indicated that the present invention was conceived and has now been reduced to practice.